Method for Optimization of Joint Arthroplasty Component Design

ABSTRACT

Methods and devices are disclosed for the optimization of shoulder arthroplasty component design through the use of computed tomography scan data from arthritic shoulders.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 14/300,805 filed Jun. 10, 2014, which is a continuation-in-partof U.S. patent application Ser. No. 13/818,738 filed Feb. 25, 2013 whichis a 371 application of PCT/US11/049686 filed Aug. 30, 2011 which claimspriority from U.S. Provisional Patent Application No. 61/379,222 filedSep. 1, 2010, and U.S. Provisional Patent Application No. 61/379,634filed Sep. 2, 2010.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for the optimization of jointarthroplasty component design, and more particularly to a method for theoptimization of shoulder arthroplasty component design through the useof computed tomography scan data.

2. Description of the Related Art

Various prostheses for the replacement of the shoulder joint are known.In one example shoulder prosthesis, the upper portion of the humerus isreplaced by a humeral component including (i) a stem that extends into abore formed within the humerus and (ii) a generally hemispherical headportion that is connected to the stem. The hemispherical head of thehumeral component articulates with a complementary concave section of aglenoid component mounted within the glenoid cavity of the scapula. Thistype of shoulder prosthesis may be called a “primary” or “total”prosthesis. In another example shoulder prosthesis, often called a“reverse” or “inverted” prosthesis, the glenoid component includes aconvex section that articulates with a complementary concave section ofthe head of the humeral component.

One alternative to total shoulder replacement is referred to as shoulderhemiarthroplasty. In one version of this procedure, the humeral head isreplaced with a generally hemispherical head that may or may not includea connected stem. The glenoid cavity of the scapula is not replaced witha glenoid component, but may be refinished in a way that gives it asmooth surface and a shape which matches the generally hemisphericalreplacement head. Another version of this procedure can use a glenoidcomponent with resurfacing of the humeral head.

Several deficiencies have been found in currently available shoulderarthroplasty systems including glenoid sizes (primary and reverse) andhumeral sizes that are not based on the anatomic distribution. Inaddition, the advent of reverse arthroplasty for the treatment ofproximal humerus fractures has also changed the requirements for anappropriate fracture stem. Specific design features are necessary tomake the fracture stem appropriate for hemiarthroplasty and reversearthroplasty use. Although resurfacing of the humerus has becomepopular, the designs are not based on an anatomic distribution. Theinstrumentation that is currently available is inadequate and may leadto significant malposition in version and inclination.

Prior magnetic resonance imaging and cadaveric studies of glenohumeralanatomy have been performed on shoulders without arthritis (Iannotti etal., “The normal glenohumeral relationships. An anatomical study of onehundred and forty shoulders”, J Bone Joint Surg Am. 1992;74:491-500;Hertel et al., “Geometry of the proximal humerus and implications forprosthetic design”, J Shoulder Elbow Surg., July/August 2002, pp.331-338; and Boileau et al., “The Three-Dimensional Geometry Of TheProximal Humerus—Implications For Surgical Technique And ProstheticDesign”, J Bone Joint Surg [Br], 1997;79-B:857-865). However, inreality, shoulder arthroplasty is not performed on normal shoulders.Shoulder arthroplasty is performed in patients with arthritis in thesetting of cartilage loss and usually associated bone loss. In order tomake properly sized implants that will accommodate patients witharthritis, it is important to understand the anatomy of these patients.

Typically, the designing surgeon has used a system with three glenoidsizes. In one study, it was determined that the distribution of glenoidcomponents used in total shoulder arthroplasty was as follows: 4% large,40% medium, and 56% small. One can see that based on component use, thesizing of these implants is not optimal. If glenoid component sizes arenot optimal, there may be issues related to perforation of the glenoidby fasteners used in attaching the glenoid component to the scapula. Inaddition, certain components may be too large for smaller patientsresulting in component overhang and potentially leading to violation ofimportant neurovascular structures. Thus, it could be hypothesized thatthe preference for small glenoid components may result from the desireto avoid glenoid perforation and/or avoid component overhang. However,larger glenoid components can lead to a better fitting prosthesis andgreater stability.

There has been increasing interest in the use of augmented glenoidcomponents in shoulder arthroplasty. Bone graft has been used in thepast to manage bone deficiency; however there has been a high rate ofgraft resorption. It has also been clearly recognized that removal ofthe remaining hard cortical bone to create a neutral surface cancompromise fixation by leaving the surgeon with only soft cancellousbone resulting in insufficient implant support for certain patients. Inaddition, excess reaming results in medialization and shortening theremaining rotator cuff lever arm with functional implications.Therefore, there has been increasing interest in the use of augmentedglenoid components.

In FIG. 5A, one example augmented glenoid component 102 for use in atotal shoulder system is shown. The glenoid component 102 has a singlecomponent plastic body 104. A concave articular surface 105 of the body104 provides a smooth bearing surface for the head portion of thehumeral component implanted into the humerus. The thickness of theplastic body 104 gradually increases from an anterior edge 106 to aposterior edge 108 thereof thereby creating a relatively smooth,arcuate-shaped medial base surface 110 from which a number of posts orpegs 112 extend. It can be seen that the augmented glenoid component 102has an augment that has a defined slope along the entire posteriorsurface of the glenoid. An augment thickness can be defined as thethickness of the posterior edge 108 minus the thickness of the anterioredge 106.

In FIG. 5B, another example augmented glenoid component 114 for use in atotal shoulder system is shown. The augmented glenoid component 114includes a body 116 having a concave articular surface 118 on one endthereof. The concave surface 118 of the body 116 provides a smoothbearing surface for the head portion of the humeral component implantedinto the humerus. The body 116 includes a step 120 on or from a bodysurface 122 opposite the concave surface 118. The step 121 forms aportion of the posterior edge 121 of the body 116. The augmented glenoidcomponent 114 also includes an anchor peg 123 and a plurality ofstabilizing posts pegs 124. It can be seen that the augmented glenoidcomponent 114 has an augment that is a step on the posterior aspect ofthe glenoid. An augment thickness can be defined as the thickness of theposterior edge 121 minus the thickness of the anterior edge 117.

In FIGS. 6A and 6B, an example augmented glenoid component 130 for usein a reverse shoulder system is shown. The glenoid component 130includes a baseplate 132 in which the thickness of the baseplate 132gradually increases from a first edge 133 to an opposite second edge 134thereof. The baseplate 132 has a surface 136 from which a peg 138extends. The baseplate 132 is secured in a glenosphere 139 forming theglenoid component 130. The glenosphere 139 has an convex articularsurface 137 that provides a smooth bearing surface for the concavearticular portion of the humeral component implanted into the humerus.An augment thickness can be defined as the thickness of the second edge134 minus the thickness of the first edge 133.

In FIGS. 6C and 6D, another example augmented glenoid component 130A foruse in a reverse shoulder system is shown. The glenoid component 130Aincludes a baseplate 132A in which the thickness of the baseplate 132Agradually increases from a first edge 133A to an approximately centralsection and then the thickness is approximately constant to an oppositesecond edge 134A thereof. The baseplate 132A has a surface 136A fromwhich a peg 138A extends. The baseplate 132A is secured in a glenosphere139A forming the glenoid component 130A. The glenosphere 139A has anconvex articular surface 137A that provides a smooth bearing surface forthe concave articular portion of the humeral component implanted intothe humerus. An augment thickness can be defined as the thickness of thefirst edge 134A minus the thickness of the second edge 133A.

However, significant deficiencies have been found in currently availableaugmented glenoid components that are not based on an anatomicdistribution. The currently available commercial designs for augmentedglenoids are not designed based on the specific dimensions of glenoidbone loss present in patients undergoing shoulder arthroplasty. In orderto make properly sized augmented glenoid components that willaccommodate patients with arthritis, it is important to understand theanatomy of these patients. One issue that continues to be raised is thatno one has ever defined on average where this transition zone beginsbetween native bone and worn bone. This would allow one to design anaugment that is shaped according to the defects that actually exist andcovers the appropriate amount of glenoid worn rather than being based onguesswork. Ideally, to design proper augmented glenoids one needs todefine the bone loss based on the anatomy of patients actuallyundergoing shoulder arthroplasty. In order to make properly sizedaugmented glenoid components that will accommodate patients witharthritis, it is important to understand the anatomy of these patients.

Thus, there exists a need for a method for the optimization of jointarthroplasty component design, and in particular, there exists a needfor a method for the optimization of shoulder arthroplasty componentdesign.

SUMMARY OF THE INVENTION

The present invention addresses the foregoing needs by providing methodsfor the optimization of joint arthroplasty component design.

In one aspect, the invention provides a method for manufacturing aprosthetic component for replacing a part of a bone of a joint in asubject. The method comprises: (a) obtaining an axial image of the boneof the joint; (b) orienting on the image a reference angle from a bodyof the bone to create a neutral face plate line that extends from afirst border of the bone to an opposite second border of the bone; (c)measuring a length of the neutral face plate line; and (d) manufacturingthe prosthetic component to include a base surface and an opposedarticular surface wherein a width of the base surface is a predeterminedpercentage of the length of the neutral face plate line. For example,the width of the base surface may be the same or less than the length ofthe neutral face plate line.

In another aspect, the invention provides a method for manufacturing aprosthetic component for replacing a part of a bone of a joint in asubject. The method comprises: (a) obtaining an axial image of the boneof the joint; (b) orienting on the image a reference angle from a bodyof the bone to create a neutral face plate line that extends from afirst border of the bone to an opposite second border of the bone; (c)orienting on the image a first reference line perpendicular to theneutral face plate line and extending over the bone in the image; (d)measuring a first reference length of the first reference line from theneutral face plate line perpendicular to a depth of a cavity in thebone; and (e) manufacturing the prosthetic component to include anarticular section and a projection extending away from the articularsection wherein a length of the projection is a predetermined percentageof the first reference length. For example, the length of the projectionis typically less than the first reference length.

In another aspect, the invention provides a method for manufacturing aglenoid component for replacing a part of a scapula of a shoulder jointin a subject, the method comprises: (a) obtaining a sagittal image ofthe glenoid of the scapula; (b) orienting on the image a first referenceline that extends perpendicularly from an inferior border of the glenoidimage over the scapula in the image; (c) orienting on the image a secondreference line that perpendicularly intersects the first reference lineand that extends from a first border of the scapula to an oppositesecond border of the scapula; (d) measuring a length of the secondreference line; and (e) manufacturing the glenoid component to have awidth that is a predetermined percentage of the length of the secondreference line. For example, the width of the glenoid component may bethe same or less than the length of the second reference line.

In another aspect, the invention provides a method for manufacturing aprosthetic component for replacing a part of a bone of a joint in asubject. The method comprises: (a) obtaining a coronal image of the boneof the joint; (b) orienting on the image a first reference line thatextends from a first border of a head of the bone to an opposite secondborder of the head of the bone; (c) orienting on the image a 90 degreereference angle from an inferior position of the first reference line tocreate a second reference line that extends over the image of the bone;(d) orienting on the image a third reference line that extends over theimage of the bone from the second reference line to a superior aspect ofa tuberosity of the bone; (e) measuring a length of the third referenceline; and (f) manufacturing the prosthetic component to include aprotruding section wherein a length of the protruding section is apredetermined percentage of the length of the reference line.

In another aspect, the invention provides a method for manufacturing aprosthetic component for replacing a part of a bone of a joint in asubject. The method comprises: (a) obtaining a coronal image of the boneof the joint; (b) orienting on the image a first reference line thatextends from a first border of a head of the bone to an opposite secondborder of the head of the bone; (c) orienting on the image a ninetydegree reference angle from an inferior position of the first referenceline to create a second reference line that extends over the image ofthe bone; (d) orienting on the image a third reference line that extendsover the image of the bone from the second reference line to a superiorborder of a tuberosity of the bone; (e) orienting on the image a fourthreference line that extends over the image of the bone from the thirdreference line to a side border of the tuberosity of the bone; (f)measuring a length of the fourth reference line; and (g) manufacturingthe prosthetic component to include a protruding section wherein adiameter of the protruding section is a predetermined percentage of thelength of the fourth reference line.

In another aspect, the invention provides a method for manufacturing aprosthetic component for replacing a part of a bone of a joint in asubject. In the method, the prosthetic component is formed to include abase surface and an opposed articular surface wherein a width of thebase surface is a predetermined percentage of a length of a neutral faceplate line. The length of the neutral face plate line used by themanufacturer in forming the prosthetic component has been determined by(i) obtaining an image of the bone of the joint, (ii) orienting on theimage a reference angle from a body of the bone to create the neutralface plate line, wherein the neutral face plate line extends from afirst border of the bone to an opposite second border of the bone, and(iii) measuring the length of the neutral face plate line. Thepredetermined percentage of the length of a neutral face plate line usedby the manufacturer in forming the prosthetic component can be 100% orless, 90%-99%, or 80%-99%. The predetermined percentage can be greaterthan, equal to, or less than 100%, and can take into account a range ofdata values observed when analyzing a number of images for themeasurement of interest. For example, the predetermined percentage canbe selected to include any number of standard deviations above a mean ofthe collected measurement data. The joint can be arthritic. In one form,at least a section of the base surface of the prosthetic component isflat. For example, the base surface of the prosthetic component can beflat around a central post that extends away from the base surface ofthe prosthetic component. The neutral face plate line can correspond toa width of a flat neutral face plate formed by removing a portion of thebone during arthroplasty. In one version of the method, the bone is thescapula, and the joint is the shoulder. The prosthetic component can bea glenoid component. The image can be a computed tomography scan slice,and the reference angle can be 90 degrees. In one version of the method,the neutral face plate line is a straight line positioned completelywithin a perimeter of the image of the bone from the first border of thebone to the second border of the bone. At least a section of thestraight line is spaced from a portion of the perimeter of the image ofthe bone, and the portion of the perimeter of the image of the bonerepresents a natural articular surface of the bone.

In another aspect, the invention provides a method for manufacturing aprosthetic component for replacing a part of a bone of a joint in asubject. In the method, the prosthetic component is formed to include anarticular section and a projection extending away from the articularsection wherein a length of the projection is a predetermined percentageof a first reference length. The first reference length used by themanufacturer in forming the prosthetic component has been determined by(i) obtaining an image of the bone of the joint, (ii) orienting on theimage a reference angle from a body of the bone to create a neutral faceplate line that extends from a first border of the bone to an oppositesecond border of the bone, (iii) orienting on the image the firstreference line, the first reference line being perpendicular to theneutral face plate line and extending over the bone in the image, (iv)measuring the first reference length of the first reference line fromthe neutral face plate line perpendicular to a depth of a cavity in thebone. The predetermined percentage of the first reference length can be100% or less, 90%-99%, or 80%-99%. The predetermined percentage can begreater than, equal to, or less than 100%, and can take into account arange of data values observed when analyzing a number of images for themeasurement of interest. For example, the predetermined percentage canbe selected to include any number of standard deviations above a mean ofthe collected measurement data. The projection can be a post. In oneversion of the method, the prosthetic component is formed such that thelength of the projection is a predetermined percentage of a secondreference length. The second reference length used by the manufacturerin forming the prosthetic component has been determined by (i) orientingon the image a second reference line parallel to the first referenceline and extending over the bone in the image, (ii) measuring the secondreference length of the second reference line from the neutral faceplate line to the depth of a cavity in the bone. In one version of themethod, the bone is the scapula, and the joint is an arthritic shoulder,and the prosthetic component is a glenoid component. The image can be acomputed tomography scan slice. In one version of the method, theneutral face plate line is a straight line positioned completely withina perimeter of the image of the bone from the first border of the boneto the second border of the bone. At least a section of the straightline is spaced from a portion of the perimeter of the image of the bone,and the portion of the perimeter of the image of the bone represents anatural articular surface of the bone.

In another aspect, the invention provides a method for manufacturing aglenoid component for replacing a part of a scapula of a shoulder jointin a subject. In the method, the glenoid component is formed to have awidth that is a predetermined percentage of a length of a secondreference line. The length of the second reference line used by themanufacturer in forming the prosthetic component has been determined by(i) obtaining an image of the glenoid of the scapula, (ii) orienting onthe image a first reference line that extends perpendicularly from aninferior border of the glenoid image over the scapula in the image, (ii)orienting on the image the second reference line, the second referenceline perpendicularly intersecting the first reference line and extendingfrom a first border of the scapula to an opposite second border of thescapula, and (iii) measuring the length of the second reference line.The predetermined percentage of the length of the second reference linecan be 100% or less, 90%-99%, or 80%-99%. The predetermined percentagecan be greater than, equal to, or less than 100%, and can take intoaccount a range of data values observed when analyzing a number ofimages for the measurement of interest. For example, the predeterminedpercentage can be selected to include any number of standard deviationsabove a mean of the collected measurement data. The second referenceline intersects the first reference line at about 10 to 18 millimetersabove the inferior border of the glenoid image. The second referenceline preferably intersects the first reference line at about 14millimeters above the inferior border of the glenoid image. The imagecan be a computed tomography scan slice.

In another aspect, the invention provides a method for manufacturing aprosthetic component for replacing a part of a bone of a joint in asubject. In the method, the prosthetic component is formed to include aprotruding section wherein a first length of the protruding section is apredetermined percentage of a length of the third reference line. Thelength of the third reference line used by the manufacturer in formingthe prosthetic component has been determined by (i) obtaining an imageof the bone of the joint, (ii) orienting on the image a first referenceline that extends from a first border of a head of the bone to anopposite second border of the head of the bone, (iii) orienting on theimage a 90 degree reference angle from an inferior position of the firstreference line to create a second reference line that extends over theimage of the bone, (iv) orienting on the image the third reference line,the third reference line extending over the image of the bone from thesecond reference line to a superior aspect of a tuberosity of the bone,and (v) measuring the length of the third reference line. In one versionof the method, the prosthetic component is formed such that a secondlength of the projection is a predetermined percentage of a fourthreference length wherein the second length of the projection isperpendicular to the first length of the projection. The fourthreference length used by the manufacturer in forming the prostheticcomponent has been determined by (i) orienting on the image a fourthreference line perpendicular to the third reference line and extendingover the bone in the image from the third reference line to a perimeterof the bone in the image, and (ii) measuring the fourth reference lineto determine the fourth reference length. In one version of the method,the bone is the humerus, the joint is the shoulder, the length of thethird reference line is a superior-inferior length of a greatertuberosity of the humerus, and the fourth reference length is amedial-lateral length of the greater tuberosity of the humerus. In oneversion of the method, the joint has been fractured, and the protrudingsection includes a plurality of fins for immobilizing fracturefragments.

In another aspect, the invention provides a method for manufacturing aprosthetic component for replacing a part of a bone of a joint in asubject. In the method, the prosthetic component is formed to include ahead and a stem connected to the head. The head has a longitudinal headaxis and the stem has a longitudinal stem axis. The head axis and thestem axis are angled to create an inclination angle between the headaxis and the stem axis. The inclination angle used by the manufacturerin forming the prosthetic component has been determined by (i) obtainingan image of the bone of the joint, (ii) orienting on the image a firstreference line that extends from a first border of a head of the bone toan opposite second border of the head of the bone, (iii) orienting onthe image a 90 degree reference angle from an inferior position of thefirst reference line to create a second reference line that extends overthe image of the bone, (iv) orienting on the image the third referenceline, the third reference line extending over the image of the bone fromthe second reference line to a superior aspect of a tuberosity of thebone, and (v) measuring an angle between the first reference line andthe third reference line, wherein the angle is equal to the inclinationangle. In one version of the method, the bone is the humerus, and thejoint is an arthritic shoulder. The image can be a computed tomographyscan slice.

In another aspect, the invention provides a method for manufacturing aprosthetic component for replacing a part of a bone of a joint in asubject. In the method, the prosthetic component is formed to include anarticular head and an opposed base surface. The head has a longitudinalhead axis, and the head axis and the base surface are angled to createan inclination angle between the head axis and the base surface. Theinclination angle used by the manufacturer in forming the prostheticcomponent has been determined by (i) obtaining an image of the bone ofthe joint, (ii) orienting on the image a first reference line thatextends from a first border of a head of the bone to an opposite secondborder of the head of the bone, (iii) orienting on the image a 90 degreereference angle from an inferior position of the first reference line tocreate a second reference line that extends over the image of the bone,(iv) orienting on the image the third reference line, the thirdreference line extending over the image of the bone from the secondreference line to a superior aspect of a tuberosity of the bone, and (v)measuring an angle between the first reference line and the thirdreference line, the angle being equal to the inclination angle. In oneversion of the method, the bone is the humerus, and the joint is anarthritic shoulder. The image can be a computed tomography scan slice.

In another aspect, the invention provides a method for manufacturing aprosthetic component for replacing a part of a bone of a joint in asubject. In the method, the prosthetic component is formed to include abody having a base surface, an outer surface opposite the base surface,a first side edge extending between the base surface and the outersurface, and a second side edge extending between the base surface andthe outer surface. The second side edge is opposite the first side edge.A first thickness of the first side edge is less than a second thicknessof the second side edge by an augment thickness. The augment thicknessis determined by (i) obtaining an image of the bone of the joint, (ii)orienting on the image a reference angle from a body of the bone tocreate a first reference line parallel to a bone surface, wherein thefirst reference line extends from a first border of the bone to anopposite second border of the bone, (iii) orienting on the image asecond reference line from the first reference line to an eroded regionof the bone surface, (iv) determining a length of the second referenceline, and (v) selecting the augment thickness based on the length of thesecond reference line. The augment thickness can be equal to the lengthof the second reference line. The image can be a computed tomographyscan axial slice, and the reference angle can be 90 degrees. The firstside edge can be an anterior edge, and the second side edge can be aposterior edge.

In one version of the method, the augment thickness extends from thesecond side edge to a location on the base surface between the firstside edge and the second side edge. The location can be determined by(vi) identifying on the image a junction between the eroded region ofthe bone surface and a native region of the bone surface, and (vii)determining a reference point on the first reference line where a thirdreference line intersects the first reference line, the third referenceline extending perpendicularly from the junction to the first referenceline. The location can be determined by (viii) calculating a percentageof a fourth reference line from the first border of the bone to thereference point with respect to a length of the first reference line,and (ix) selecting the percentage to be an amount of the body having theaugment thickness.

In one version of the method, the augment thickness increases from thefirst side edge to the second side edge thereby defining an augmentangle between the outer surface and the base surface. The augment anglecan be determined by orienting on the image an angle reference line fromthe first border to where the second reference line intersects the bonesurface and by selecting the augment angle as an angle between the firstreference line and the angle reference line.

In one version of the method, the augment thickness increases from thefirst side edge to the second side edge at a step discontinuity.

The bone can be the scapula, the joint can be the shoulder, and theprosthetic component can be a glenoid component. The outer surface canbe a concave bearing surface for articulating with a humeral headcomponent of a total shoulder arthroplasty system. The glenoid componentcan be a glenoid baseplate dimensioned to be secured to a glenosphere ofa reverse shoulder arthroplasty system.

In another aspect, the invention provides a method for manufacturing aprosthetic component for replacing a part of a bone of a joint in asubject. In the method, the prosthetic component is formed to include abody having a base surface, an outer surface opposite the base surface,a first side edge extending between the base surface and the outersurface, and a second side edge extending between the base surface andthe outer surface wherein the second side edge is opposite the firstside edge. A first thickness of the first side edge is less than asecond thickness of the second side edge by an augment thickness. Theaugment thickness can be determined by (i) obtaining an image of thebone of the joint, (ii) orienting on the image a neutral face plateline, (iii) orienting on the image a first reference line, the firstreference line being parallel or within 20 degrees of parallel to theneutral face plate line, the first reference line extending from a firstborder of the bone to an opposite second border of the bone, (iv)orienting on the image a second reference line from the first referenceline to a bone surface, the second reference line intersecting the firstreference line a predetermined distance from the first border of thebone, (v) determining a length of the second reference line, and (vi)selecting the augment thickness based on the length of the secondreference line. The augment thickness can be equal to the length of thesecond reference line.

In one version of the method, the augment thickness extends from thesecond side edge to a location on the base surface between the firstside edge and the second side edge. The location can be determined by(vii) identifying on the image a junction between the eroded region ofthe bone surface and a native region of the bone surface, and (viii)determining a reference point on the first reference line where a thirdreference line intersects the first reference line, the third referenceline extending perpendicularly from the junction to the first referenceline. The location can be determined by (viii) calculating a percentageof a fourth reference line from the first border of the bone to thereference point with respect to a length of the first reference line,and (ix) selecting the percentage to be an amount of the body having theaugment thickness.

In one version of the method, the augment thickness increases from thefirst side edge to the second side edge thereby defining an augmentangle between the outer surface and the base surface, and the augmentangle can be determined by orienting on the image an angle referenceline from the first border to where the second reference line intersectsthe bone surface and by selecting the augment angle as an angle betweenthe first reference line and the angle reference line. The augmentthickness may increase from the first side edge to the second side edgeat a step discontinuity.

In the method, the bone can be the scapula, the joint can be theshoulder, and the prosthetic component can be a glenoid component. Theouter surface can be a concave bearing surface for articulating with ahumeral head component of a total shoulder arthroplasty system. Theglenoid component can be a glenoid baseplate dimensioned to be securedto a glenosphere of a reverse shoulder arthroplasty system.

In one version of the method, the image is a computed tomography scancoronal slice. The first reference line can be about 10 degrees fromparallel to the neutral face plate line. In one version of the method,the first side edge of the prosthetic component body is an inferioredge, and the second side edge is a superior edge. The predetermineddistance can be about 20 millimeters to about 40 millimeters.

In another aspect, the invention provides a method for manufacturing aprosthetic component for replacing a part of a bone of a joint in asubject. In the method, the prosthetic component is formed to include abody having a base surface, an outer surface opposite the base surface,a first side edge extending between the base surface and the outersurface, and a second side edge extending between the base surface andthe outer surface wherein the second side edge is opposite the firstside edge. A first thickness of the first side edge is less than asecond thickness of the second side edge by an augment thickness. Theaugment thickness increases from the first side edge to the second sideedge thereby defining an augment angle between the outer surface and thebase surface. The augment angle can be determined by (i) obtaining animage of the bone of the joint, (ii) orienting on the image a neutralface plate line, (iii) orienting on the image a first reference line,the first reference line being parallel to the neutral face plate line,the first reference line extending from a first border of the bone to anopposite second border of the bone, (iv) orienting on the image a secondreference line from the first reference line to a bone surface, thesecond reference line intersecting the first reference line apredetermined distance from the first border of the bone, (v) orientingon the image an angle reference line from the first border to where thesecond reference line intersects the bone surface, and (vi) selectingthe augment angle based on a measured angle between the first referenceline and the angle reference line. The image can be a computedtomography scan coronal slice.

In one version of the method, when the measured angle is in the range of0 to 10 degrees superior tilt, the augment angle is selected as about 10degrees. In another version of the method, when the measured angle isbetween 10 and 15 degrees superior tilt, the augment angle is selectedas about 15 degrees. In another version of the method, when the measuredangle is in the range of 15 to 20 degrees superior tilt, the augmentangle is selected as about 20 degrees.

In one version of the method, the bone is the scapula, the joint is theshoulder, and the prosthetic component is a glenoid component. Theglenoid component can be a glenoid baseplate dimensioned to be securedto a glenosphere of a reverse shoulder arthroplasty system. The firstside edge of the prosthetic component body can be an inferior edge, andthe second side edge can be a superior edge.

The methods of the present disclosure can be used in a number ofdifferent joints in addition to the shoulder. For example, the methodsmay be used in the elbow, wrist, hand, spine, hip, knee, ankle, and/orfoot. When the joint is the elbow, the bone can be selected from theulna, radius, and humerus. When the joint is the wrist, the bone can beselected from the radius, ulna, and carpal bones. When the joint is thehand, the bone can be selected from phalanges, metacarpals, and carpals.When the joint is the spine, the bone can be a vertebrae. When the jointis the hip, the bone can be selected from the femur and thepelvis/acetabulum. When the joint is the knee, the bone is selected fromthe femur, tibia and patella. When the joint is the ankle, the bone canbe selected from the talus, the tibia and the fibula. When the joint isthe foot, the bone can be selected from phalanges tarsals andmetatarsals.

The method of the present disclosure allows one to design an augmentthat is shaped according to the defects that actually exist and coversthe appropriate amount of glenoid worn rather than being based onguesswork. This disclosure facilitates design in three ways: (1) itdefines the angle of glenoid erosion; (2) it defines the depth ofglenoid erosion; and (3) it defines what percent of the glenoid has aneroded surface. This information will significantly improve the abilityto design an augmented glenoid component.

These and other features, aspects, and advantages of the presentinvention will become better understood upon consideration of thefollowing detailed description, drawings, and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of one embodiment of a shoulderprosthesis suitable for use in the invention.

FIG. 2 shows a tracing of a computed tomography (CT) axialtwo-dimensional (2D) CT slice of the scapula and humerus withmeasurement lines according to the invention shown in broken lines.

FIG. 3 shows a tracing of a 2D CT sagittal slice of the scapula withmeasurement lines according to the invention shown in broken lines.

FIG. 4 shows a tracing of a CT 2D coronal slice of the scapula andhumerus with measurement lines according to the invention shown inbroken lines.

FIG. 5A is a side sectional view of a prior art augmented glenoidcomponent.

FIG. 5B is a side view of another prior art augmented glenoid component.

FIG. 6A is an exploded side view of yet another prior art augmentedglenoid component.

FIG. 6B is a side view the augmented glenoid component of FIG. 6A in theassembled configuration.

FIG. 6C is an exploded side view of yet another prior art augmentedglenoid component.

FIG. 6D is a side view the augmented glenoid component of FIG. 6C in theassembled configuration.

FIG. 7 shows a tracing of a computed tomography (CT) axialtwo-dimensional (2D) CT slice of the scapula and humerus withmeasurement lines according to the invention shown in broken lines.

FIG. 8 shows a tracing of a 2D CT coronal slice of the scapula withmeasurement lines according to the invention shown in broken lines.

FIG. 9 shows another tracing of a CT 2D coronal slice of the scapula andhumerus with measurement lines according to the invention shown inbroken lines.

Like reference numerals will be used to refer to like parts from Figureto Figure in the following description of the drawings.

DETAILED DESCRIPTION OF THE INVENTION

Looking first at FIG. 1, there is shown one example embodiment of ashoulder prosthesis 10 suitable for use in the invention. The upperportion of the humerus 12 is replaced by a humeral component 14including a stem 16 that extends into a bore formed within the humerus12. Typically, the stem 16 is fixed within the bore formed within thehumerus 12. The stem 16 has a longitudinal stem axis S. A generallyhemispherical head 18 is connected to the stem 16. The stem 16 can bemonolithic with the head 18, or the stem 16 and the head 18 can formedas separate parts. The hemispherical head 18 has a base surface 19 and alongitudinal head axis H. The hemispherical head 18 of the humeralcomponent 14 articulates with a complementary concave section 22 of aglenoid component 24 that is fixed within the glenoid cavity of thescapula 26 (shown cutaway) using cemented or uncemented posts 28. Theglenoid component 24 includes a base surface 27 opposite the concavesection 22 that serves as an articular surface of the glenoid component24.

Proper design and selection of the hemispherical head 18 and the glenoidcomponent 24 can be achieved using the method of the invention. In onenon-limiting example method of the invention, eleven measurements areobtained using CT slices. The eleven measurements are as follows: (1)glenoid version; (2) anterior-posterior (AP) diameter at the articularsurface; (3) anterior-posterior width at a neutral face plate; (4) depthof the glenoid vault from a neutral face plate; (5) depth of the glenoidvault from a neutral face plate with a diameter of the center post (anexample center post diameter being five millimeters); (6)superior-inferior glenoid height; (7) determination of theanterior-posterior width fourteen millimeters from the inferior borderof the glenoid; (8) humeral head diameter; (9) humeral head thickness;(10) greater tuberosity length of the humerus; (11) greater tuberositywidth of the humerus; and (12) humeral inclination.

Proper design and selection of an augmented glenoid component can beachieved using the method of the invention. In one non-limiting examplemethod of the invention, measurements are obtained using CT slices asshown in FIGS. 7-9.

The degree of anterior-posterior glenoid wear has been defined in aseries of patients undergoing shoulder arthroplasty. This angle allowsone to determine a specific anatomic range of augments to accommodateanterior-posterior bone loss in patients undergoing anatomic totalshoulder arthroplasty and reverse shoulder arthroplasty.

Superior glenoid wear may occur in patients with rotator cuffinsufficiency undergoing reverse shoulder arthroplasty. Previously,there was no information on the specific range of inferior-superiorglenoid wear among these patients. Therefore, in order to design aglenoid baseplate that accommodates the anatomy of these patients andallows for proper fit with minimal bone removal, it is critical tounderstand the anatomic distribution in these patients. Thus, a methodhas been developed and utilized among patients who have undergonereverse arthroplasty of the shoulder to determine the anatomicdistribution. The concept of superior wear angle and depth expands andis an extension on the neutral face plate concept described herein.

The most frequently used glenoid baseplate in the United States has adiameter of 25 millimeters. Therefore, one may determine the angle of anaugmented glenoid component by placing an angle to the most medialaspect of the glenoid 25 millimeters from the inferior aspects of theglenoid compared to one parallel to the faceplate of the glenoid.However, the method is not limited to 25 millimeter diameter circularbaseplates. One may determine the angle of an augmented glenoidcomponent by placing an angle to the most medial aspect of the glenoidabout 20 to about 40 millimeters from the inferior aspects of theglenoid compared to one parallel to the faceplate of the glenoid. Thiswould accommodate circular baseplates having a 20-40 millimeterdiameter, or oval baseplates having a major axis up to 40 millimeters.In cases where superior glenoid erosion has resulted in loss of thesuperior aspect of the glenoid, the scapular spine can be used with astandardized population based average to determine the inclination planeof the glenoid face.

Various combinations of these measurements are used for manufacturing aprosthetic component for replacing a part of a bone of a joint in asubject (e.g., mammal). The prosthetic component may be formed from, forexample: (i) a metal or metal alloy such as a titanium alloy (e.g.,titanium-6-aluminum-4-vanadium), a cobalt alloy, a stainless steelalloy, or tantalum; (ii) a nonresorbable ceramic such as aluminum oxideor zirconia; (iii) a nonresorbable polymeric material such aspolyethylene; or (iv) a nonresorbable composite material such as acarbon fiber-reinforced polymers (e.g., polysulfone). The prostheticcomponent can be manufactured by machining an article formed from thesematerials, or by molding these materials in a suitable mold.

EXAMPLES

The following Examples have been presented in order to furtherillustrate the invention and are not intended to limit the invention inany way.

Example A 1. Glenoid Version

Using an axial 2D CT scan of a human shoulder, the mid point of theglenoid was determined. A first line was then drawn through the midpointand parallel to the scapular body. The first line intersects a secondline drawn parallel to the joint surface. The glenoid version was theangle between the first line and the second line, and was recorded indegrees.

2. Anterior-Posterior (AP) Width At The Articular Surface

Using an axial 2D CT scan of a human shoulder, the diameter (AP width)was measured at the mid-point of the glenoid in millimeters.

3. Anterior-Posterior (AP) Width At A Neutral Face Plate

Looking at FIG. 2, an axial 2D CT scan of a human shoulder was obtainedand a 90 degree angle A (shown in broken lines) was oriented from thescapular body 26 and then placed on the glenoid 30 to create a neutralface plate 32 (shown in broken lines) that runs from one side border 34to the other side border 36 of the glenoid 30. This width was thenmeasured in millimeters. This measurement is important to determine thetrue AP width of the glenoid after creating a flat neutral face plate byremoving bone during arthroplasty. This is what occurs at surgeryaccording to the method of the invention, yet this measurement has neverbeen previously described. Prior measurements have been made of thearticular surface only of the glenoid. This explains why many glenoidcomponent sizes are too large. The measurement at a neutral faceplate isusually several millimeters less than the measurement at the articularsurface due to reaming or removing glenoid bone to make the surface flatto place the glenoid component 24.

When manufacturing a glenoid component, a manufacturer can be suppliedwith the length of the neutral face plate 32 which provides a true APwidth of the glenoid after creating a flat neutral face plate byremoving bone during arthroplasty. A predetermined percentage of thelength of the neutral face plate 32 can be used to machine or mold theglenoid component to have a selected width for the base surface 27 (seeFIG. 1).

4. Depth of the Glenoid Vault from a Neutral Face Plate

Still looking at FIG. 2, a line 38 (shown in broken lines) was startedat the neutral face plate 32 and was drawn medially to determine thedepth of the glenoid vault 40. Previous reports have mentioned only thedepth from the articular surface which overstates the depth of theglenoid. This explains why many central posts or peripheral pegs ofglenoid components that are currently in the market are too long andperforate the glenoid. Prior designs have not been designed based onpatients with arthritis and associated bone loss who have undergoneshoulder arthroplasty.

When manufacturing a glenoid component, a manufacturer can be suppliedwith the length of the line 38. A predetermined percentage of the lengthof the line 38 can be used to machine or mold the glenoid component tohave a selected longitudinal length for the post 28 (see FIG. 1).

5. Depth of the Glenoid Vault from a Neutral Face Plate with a Diameterof 5 Millimeters

Still looking at FIG. 2, a five millimeter line 42 (shown in brokenlines) was placed within the vault parallel to the line 38. This willshow one the depth of the glenoid vault that one can drill back to afive millimeter diameter. This allows accurate determination of the safelength for a central post or screw. Other post diameters are allowed inthe design, five millimeters is used only as an example.

When manufacturing a glenoid component, a manufacturer can be suppliedwith the length of the line 42. A predetermined percentage of the lengthof the line 42 can be used to machine or mold the glenoid component tohave a selected length for the post 28 (see FIG. 1).

6. Superior-Inferior Glenoid Length

The height of the glenoid was measured in millimeters.

7. Determination Of The AP Width Fourteen Millimeters From The InferiorBorder Of The Glenoid

Turning to FIG. 3, a 2D CT scan of a human shoulder was obtained and onthe sagittal cut, an anterior-posterior width on line 46 (shown inbroken lines) was measured. Line 46 was perpendicular to and fourteenmillimeters up line 50 (shown in broken lines) from the inferior border48 of the glenoid 30. This measures the anterior-posterior width of theglenoid fourteen millimeters above the inferior rim of the glenoid. Thisallows determination of the appropriate width of a glenoid base platefor reverse arthroplasty.

When manufacturing a glenoid component, a manufacturer can be suppliedwith the length of the line 46. A predetermined percentage of the lengthof the line 46 can be used to machine or mold the glenoid component tohave a selected width for the base surface 27 (see FIG. 1).

8. Humeral Head Diameter and 9. Humeral Head Thickness

Turning to FIG. 4, a 2D CT scan of a human shoulder was obtained and onthe coronal slice the diameter of the humeral head was measured inmillimeters at line 52 (shown in broken lines). A line 54 (shown inbroken lines) was then drawn perpendicular from line 52 to the surface56 of the humeral head. The length of line 54 (here measured inmillimeters) gives one the thickness of the humeral head.

10. Greater Tuberosity Length and 11. Greater Tuberosity Width

A 90 degree line 58 (shown in broken lines) was taken off the mostinferior aspect of the humeral head cut. A line 62 (shown in brokenlines) was then placed from the superior aspect of the greatertuberosity (intersection with the superior end point of line 52) tointersect this line 58. This line 62 shows the true distance of thegreater tuberosity in length (superior-inferior). Next a line 64 (shownin broken lines) was taken 90 degrees to this line 62 to show themaximum diameter of the greater tuberosity. This line 64 shows the truedistance of the greater tuberosity in width (medial-lateral). Thisfacilitates designing a humeral component that maximizes tuberosityhealing as well as anatomic component shape. This data also facilitatesthe design of different size humeral components specifically forfracture cases to improve tuberosity healing. This would includedifferent size “fins” or other components to accommodate and securefracture fragments based on the size of the patient.

12. Measurement of Humeral Inclination

On FIG. 4, taking the angle B between lines 52 and 62 in degrees andadding 90° defines the inclination angle of the humeral head in degrees(i.e., angle B in degrees +90°=the inclination of the humeral head).This measurement can determine the true range of inclination necessaryfor humeral component design.

When manufacturing a humeral component, a manufacturer can be suppliedwith the inclination angle of the humeral head. The inclination angle ofthe humeral head can be used to machine or mold the humeral component tohave a selected angle, or a selected range of angles (for adjustablehumeral inclination) between the longitudinal head axis H (see FIG. 1)and the longitudinal stem axis S (see FIG. 1) or the longitudinal headaxis H and the base surface 19 (see FIG. 1).

Results

Using the measurement technique of Examples 1-12, a review of 800patients who have undergone shoulder arthroplasty (436 total shoulderarthroplasties, 210 reverse shoulder arthroplasties, and 154hemiarthroplasties) was completed and is shown in Table 1 below. Inaddition, statistical analysis revealed that when evaluating forspecific anatomic ratios there were very tight confidence intervals.This can be further used to ensure proper component design as shown inTable 2.

TABLE 1 Anatomic Measurements of 800 Shoulders Variable Mean Std DevMedian Minimum Maximum 10th Pctl 90th Pctl 1. Glenoid version (degrees)10.66 9.68 10.00 −27.00 49.00 0.00 24.00 2. AP width at articularsurface (mm) 28.71 4.32 28.50 12.40 41.20 23.30 34.20 3. AP width at aneutral faceplate (mm) 24.59 3.83 24.70 12.00 36.90 19.80 29.30 4. Vaultdepth from a neutral face plate (mm) 21.79 4.30 22.00 6.10 37.00 16.3027.20 5. Vault depth to a 5 mm diameter (mm) 16.07 4.2 16.30 2.00 27.3010.80 21.50 6. Superior-Inferior: Glenoid Height (mm) 34.61 4.4 34.2024.00 50.10 29.10 40.60 7. AP width 14 mm from inferior glenoid rim (mm)26.78 3.14 26.80 15.00 35.20 22.80 30.80 8. Humeral head diameter (mm)43.47 4.31 43.00 32.80 56.00 38.30 49.60 9. Humeral head thickness (mm)22.11 2.76 22.20 14.20 29.70 18.80 25.60 10. Greater tuberositysuperior-inferior (mm) 33.61 4.54 33.10 21.00 47.00 28.00 40.00 11.Greater tuberosity medial-lateral (mm) 11.29 2.01 11.00 6.30 18.00 8.9014.00 12. Humeral Inclination (degrees) 129.13 5.72 129.00 115.00 145.00121.00 137.00 The 10th and 90th percentile refer to the range of data.

TABLE 2 Overall - 95% Overall Confidence Ratio Ratio Intervals Humeralhead diameter/Humeral head 1.98 1.97, 2.00 thickness Greater tuberositymedial-lateral (width)/ 0.337 0.334, 0.341 Greater tuberositysuperior-inferior (height) AP width at a neutral faceplate/Vault 1.161.14, 1.18 depth from a neutral faceplate

Example B

Glenoid wear typically occurs in a posterior pattern with osteoarthritisand a superior direction with rotator cuff insufficiency. Anterior wearmay also occur as well as combined patterns, however posterior orsuperior wear patterns are the dominant wear patterns.

There are two primary means to resurface a worn glenoid component:anatomic shoulder arthroplasty and reverse arthroplasty. Anatomicarthroplasty is typically done in the setting of a posterior wearpattern. Reverse arthroplasty may be done in a posterior or superiorwear pattern. In order to design appropriately sized augmentedcomponents, one needs to know the dimensions of wear.

1. Design Of An Augment For A Posteriorly Worn Glenoid

The angle of the augment is determined by determining the version of theglenoid. Looking at FIG. 7, an axial 2D CT scan of a human shoulder wasobtained. One orients a line 231 parallel to the scapular body 226 thatintersects a line 232 parallel to the joint surface at 90 degree angleA2. The line 232 runs at least from a posterior side border 234 to ananterior side border 236 of the glenoid 230. The thickness dimension ofthe augment is determined by measuring along line 238 in millimeters theamount of wear of the posterior aspect of the glenoid 230. One can alsodetermine where the junction 241 occurs between native bone and erodedbone. This facilitates design of the augment by determining what percentof the glenoid 230 should have an augmented surface. For example, adistance along line 232 from the posterior side border 234 to theanterior side border 236 can be determined, and then a distance alongline 232 from the anterior side border 236 to a point P at a line 243passing through the junction 241 and perpendicular to the line 232. Anaugment angle can be determined from angle G between line 232 and anangle reference line 239 from the anterior side border 236 to the line238 where line 238 intersects the bone. The thickness of the augment,angle, and percent of surface covered by the augment may be lessdepending on the amount that the surgeon would want to ream the glenoid.However, reaming weakens the bone as well as decreases the moment armfor the rotator cuff muscles. Therefore, there has been increasinginterest for the use of augments rather than reaming glenoid bone.

2. Design Of An Augment For A Superiorly Worn Glenoid.

Looking at FIG. 8, a coronal 2D CT scan of a human shoulder wasobtained. One determines the thickness of an augment needed by measuringa set distance from the inferior part 242 of the glenoid 230. Forexample, for a glenoid baseplate that is 25 millimeters in diameter, onecan measure 25 millimeters (as dimension D of FIG. 8) from the inferiorpart 242 of the glenoid 230 along a line 244 parallel to the neutralface plate 246 of the glenoid 230 for a baseplate placed in neutraltilt. One can then measure medially along line 248 from the line 244 tothe bone surface to determine the thickness of the superior augmentneeded. One can determine the angle of an augmented glenoid by placing aline 249 creating an angle A3 to the most medial aspect of the glenoid230 compared to the line 244 parallel to the neutral face plate 246 ofthe glenoid 230. One can also determine where the junction 251 occursbetween native bone and eroded bone. This facilitates design of theaugment by determining what percent of the glenoid should have anaugmented surface. For example, a distance along line 244 from theinferior part 242 to the superior side border 256 can be determined, andthen a distance along line 244 from the inferior part 242 to a point P1at a line 253 passing through the junction 251 and perpendicular to theline 244.

One can create a glenoid component with 10 degrees of inferior tilt aspreferred by some surgeons. Looking at FIG. 9, a coronal 2D CT scan of ahuman shoulder was obtained. One determines the thickness of an augmentneeded by measuring a set distance from the inferior part 342 of theglenoid 230. For example, for a glenoid baseplate that is 25 millimetersin diameter, one can measure 25 millimeters (as dimension D of FIG. 9)from the inferior part 342 of the glenoid 230 along a line 344 that has10 degrees of tilt with respect to the neutral face plate 346 of theglenoid 230 for a baseplate placed in 10 degrees of inferior tilt. Onecan then measure medially along line 348 from the line 344 to the bonesurface to determine the thickness of the superior augment needed. Onecan determine the angle of an augmented glenoid by placing a line 349creating an angle A4 to the most medial aspect of the glenoid 230compared to the line 344. One can also determine where the junction 351occurs between native bone and eroded bone. This facilitates design ofthe augment by determining what percent of the glenoid should have anaugmented surface. For example, a distance along line 344 from theinferior part 342 to the superior side border 356 can be determined, andthen a distance along line 344 from the inferior part 342 to a point P2at a line 353 passing through the junction 351 and perpendicular to theline 344.

3. Glenoid Wear Patterns

In a series of 50 consecutive shoulders that underwent reversearthroplasty, CT scans indicated that there were 28 with no superiorglenoid wear (56%) and 22 with superior glenoid wear (44%). Among theglenoids without wear, superior inclination averaged 8 degrees. Amongthe glenoids with superior wear, there were 3 with mild wear with 5-10degrees superior inclination, 10 with moderate wear with 10-15 degreessuperior inclination, and 9 with severe wear with greater than 15degrees of superior inclination. Among the 9 with severe wear, two hadwear greater than 20 degrees.

This study revealed a high rate of superior glenoid wear in patientsundergoing reverse arthroplasty (44%). The data derived from this methodhas provided insight for the range of augments necessary to accommodatepatients undergoing reverse arthroplasty.

The methodology has revealed the potential benefit of an augmentedglenoid baseplate for the reverse arthroplasty not only in the settingof significant glenoid erosion but also in the patient with no glenoiderosion. An augmented glenoid can facilitate the inferior tilting of theglenoid component to decrease the chance of loosening—while maintainingbetter quality bone and preserving bone.

Among shoulders with no wear, there was on average 8 degrees of superiortilt. A preferred amount of inferior inclination is approximately 10degrees. One strategy would allow the surgeon to ream the glenoid to aneutral position and then use a 10 degree augmented glenoid to createthe appropriate tilt. This allows the surgeon to provide optimalinferior tilt without removing more inferior bone—a bone preservingapproach. This is particularly important in a large glenoid with a deepconcavity. If an augmented glenoid is not used, an excessive amount ofglenoid reaming may be necessary to create the appropriate inferiortilt.

The method has also revealed that augments ranging up to 20 degrees canaccommodate 96% of glenoids undergoing reverse arthroplasty without theneed for bone grafting. In a deformity up to 20 degrees, the surgeon canream back to 10 degrees of superior tilt and use an augment with a 20degree angle. This would create 10 degrees of inferior tilt. This methodhas also facilitated creation of an algorithm to manage superior glenoidwear. See Table 3 below.

TABLE 3 Reverse Shoulder-Glenoid Bone Preserving Technique InclinationGlenoid Wear Correction Treatment Outcome Slight or no wear up to 10degrees 10 degree augmented 10 degrees (0-10 degrees glenoid inferiortilt superior tilt) Moderate wear up to 10 degrees 15 degree augmented10 degrees (10-15 degrees) glenoid inferior tilt Severe wear up to 10degrees 20 degree augmented 10 degrees (15-20 degrees) glenoid inferiortilt

Use of the method described herein for superior wear and inclination hasrevealed the optimum range of augments necessary for reverse shoulderarthroplasty with a superior wear pattern. In addition, this method hashelped identify a bone preserving technique of placing the glenoidbaseplate in patients with minimal to no wear.

Thus, the invention provides a method for the optimization of shoulderarthroplasty component design. Use of this method and the data that itprovides gives unique insight into the number, size and shape of glenoidcomponents for total shoulder arthroplasty and reverse shoulderarthroplasty as well as humeral heads for shoulder arthroplasty andresurfacing arthroplasty. This method also provides valuable informationfor the optimal design, shape, and size of the proximal humeral body fora fracture stem to maximize tuberosity healing and humeral componentdesign for hemiarthroplasty/total shoulder arthroplasty. A method forthe optimization of an augmented glenoid design for shoulderarthroplasty is also provided. In the course of new product development,this method is a valuable resource that can be used to radiographicallyevaluate each new component design to ensure optimal fit prior tocomponent production and product launch. While the invention isdescribed herein as a method for the optimization of shoulderarthroplasty component design, it can be used for other joints (e.g.,elbow, wrist, hand, spine, hip, knee, ankle, foot, etc. . . . ).

Although the present invention has been described in detail withreference to certain embodiments, one skilled in the art will appreciatethat the present invention can be practiced by other than the describedembodiments, which have been presented for purposes of illustration andnot of limitation. Therefore, the scope of the appended claims shouldnot be limited to the description of the embodiments contained herein.

What is claimed is:
 1. A method for manufacturing a prosthetic componentfor replacing a part of a bone of a joint in a subject, the methodcomprising: forming the prosthetic component to include a body having abase surface, an outer surface opposite the base surface, a first sideedge extending between the base surface and the outer surface, and asecond side edge extending between the base surface and the outersurface, the second side edge being opposite the first side edge,wherein a first thickness of the first side edge is less than a secondthickness of the second side edge by an augment thickness, the augmentthickness having been determined by (i) obtaining an image of the boneof the joint, (ii) orienting on the image a neutral face plate line,(iii) orienting on the image a first reference line, the first referenceline being parallel or within 20 degrees of parallel to the neutral faceplate line, the first reference line extending from a first border ofthe bone to an opposite second border of the bone, (iv) orienting on theimage a second reference line from the first reference line to a bonesurface, the second reference line intersecting the first reference linea predetermined distance from the first border of the bone, (v)determining a length of the second reference line, and (vi) selectingthe augment thickness based on the length of the second reference line.2. The method of claim 1 wherein: the augment thickness extends from thesecond side edge to a location on the base surface between the firstside edge and the second side edge.
 3. The method of claim 2 wherein:the location is determined by (vii) identifying on the image a junctionbetween the eroded region of the bone surface and a native region of thebone surface, and (viii) determining a reference point on the firstreference line where a third reference line intersects the firstreference line, the third reference line extending perpendicularly fromthe junction to the first reference line.
 4. The method of claim 3wherein: the location is determined by (viii) calculating a percentageof a fourth reference line from the first border of the bone to thereference point with respect to a length of the first reference line,and (ix) selecting the percentage to be an amount of the body having theaugment thickness.
 5. The method of claim 1 wherein: the augmentthickness increases from the first side edge to the second side edgethereby defining an augment angle between the outer surface and the basesurface, and the augment angle is determined by orienting on the imagean angle reference line from the first border to where the secondreference line intersects the bone surface and by selecting the augmentangle as an angle between the first reference line and the anglereference line.
 6. The method of claim 1 wherein: the augment thicknessincreases from the first side edge to the second side edge at a stepdiscontinuity.
 7. The method of claim 1 wherein: the bone is thescapula, the joint is the shoulder, and the prosthetic component is aglenoid component.
 8. The method of claim 7 wherein: the outer surfaceis a concave bearing surface for articulating with a humeral headcomponent of a total shoulder arthroplasty system.
 9. The method ofclaim 7 wherein: the glenoid component is a glenoid baseplatedimensioned to be secured to a glenosphere of a reverse shoulderarthroplasty system.
 10. The method of claim 1 wherein: the image is acomputed tomography scan coronal slice.
 11. The method of claim 1wherein: the first reference line about 10 degrees from parallel to theneutral face plate line.
 12. The method of claim 1 wherein: the firstside edge is an inferior edge, and the second side edge is a superioredge.
 13. The method of claim 1 wherein: the predetermined distance isabout 20 millimeters to about 40 millimeters.
 14. The method of claim 1wherein: the augment thickness is equal to the length of the secondreference line.
 15. The method of claim 1 wherein the joint is selectedfrom elbow, wrist, hand, spine, hip, knee, ankle, and foot.
 16. Themethod of claim 15 wherein: when the joint is the elbow, the bone isselected from the ulna, radius and humerus, when the joint is the wrist,the bone is selected from the radius, ulna and carpal bones when thejoint is the hand, the bone is selected from phalanges, metacarpals, andcarpals, when the joint is the spine, the bone is a vertebrae, when thejoint is the hip, the bone is selected from the femur and the pelvis,when the joint is the knee, the bone is selected from the femur, tibia,and patella when the joint is the ankle, the bone is selected from thetalus, the tibia and the fibula, and when the joint is the foot, thebone is selected from phalanges, tarsals, and metatarsals.